Photoinduced electron transfer at liquid/liquid interfaces. Part V. Organisation of water-soluble chlorophyll at the water/1,2-dichloroethane interface

The molecular organisation and photoreactivity of water-soluble chlorophyll (CHL) are studied at the polarisable water/1,2-dichloroethane interface via photocurrent measurements. In the presence of ferrocene in the organic phase, photocurrent responses were observed as a result of the heterogeneous quenching of adsorbed CHL species. The magnitude of the photoresponses increases with increasing Galvani potential differences with respect to the organic phase. The photocurrent dependence on the bulk concentration of CHL indicated that the dye exhibits a strong affinity for the liquid/liquid junction. Furthermore, the behaviour of the photoresponses as a function of the Galvani potential difference suggests that partial protonation of the peripheral carboxyl groups takes place at the interface, decreasing the overall charge of the adsorbed species. The average molecular orientation of the adsorbed CHL was estimated from photocurrent measurement employing linearly polarised light under total internal reflection. It was observed that the preferential molecular orientation was fairly independent of the applied potential and surface coverage. It is suggested that the interfacial stabilisation of CHL is determined by amphiphilic properties arising from the non-symmetric distribution of the peripheral carboxyl groups.